A Question About Gaming on a Laptop

I have a laptop that I have been using for gaming. The laptop isn't extremely powerful but it is good enough that I can run most console ports at a slightly higher resolution and with more features on then what would be capable on an Xbox 360 and PS3. Here are my specs:

Windows 7 64-bit

8 GB of ram

AMD A8-3500 M APU (It's a quad-core CPU with 1.5 Ghz per core)

450 GB SSD with 150 GB free

AMD Radeon HD 6620G

So my laptop won't set the PC world on fire. But I've noticed that, while I can run most games at a quality slightly above the Xbox 360 and PS3, some games I can run really, really well and others I can barely run at all. I'm curious as to why this is. For example, Sleeping Dogs, with the high resolution texture pack and with most things on high at 1280x768, runs between 30-60 fps. Trine 2 runs at 1280x768 at the very high setting and with anti-aliasing on 4X runs at nearly 60 fps with very few hitches. But Saints Row the Third, which was supposed to be a really good port, runs like shit on my system. Even with everything on low at 1280x768 I can barely get a steady 30 fps. The only thing I can think of is that Saints Row requires more of the graphics capabilities of my laptop whereas Sleeping Dogs and Trine 2 utilizes the stronger components of my computer. Does that sound accurate? What else could cause this difference? Is there something I could do to optimize my computer beyond the normal cleaning we all do?

You just can't go in with the logic that "Oh this looks similar or comparable, so it should run the same" there's no easy explanation to it, some engines/games also just run better on ATi (not usually) and others Nvidia, so there's that to consider too.

Crysis from 2007 looks better than 99% of games and yet is easier to run than most coming out these days.

and Trine 2 really isn't a fair comparison to open world games like Sleeping Dogs or Saints Row, games that operate on the 2D pane are pretty much always less demanding and Trine has a whole lot less going on than those two.

Edit:

Q6600 @ 3.6 (8x450)
HD5870 (11.4 and 11.10 drivers)
4GB RAM (5-5-5-18 @ 900)
Terrible performance in open areas. 10-20 while driving, 15-30 running around.
If I am an enclosed area, eg inside a building with no view of the outside, it runs at an acceptable 60fps ...
Tried every preset setting from DX9 Low @ 1280x720 to DX11 Ultra @ 1920x1200 and performance is similar in all modes.
I was starting to think it was just me ...

If this is still accurate it seems Saints Row doesn't play very nice with ATi (surprise surprise) - http://forums.steampowered.com/forums/showthread.php?t=2232730

I play games on a laptop with specs in a similar range to yours. What I've figured is that it all comes down to how well optimized the game is for lower end graphics. I'm also on an ATI video card but I've found in general most games tend to run better on Nvidia's of similar specs.

I think there's something funky with Saint's Row The Third's trees. Being in an area with trees seemed to cut my framerate in half. Different games are certainly going to give you different performance even if they look similar. Both Saint's Row and Sleeping Dogs are open world games and so they naturally demand more power than say an on rails shooter. 
 
High Res textures will require more memory but a lot of physics will need more processing power that Saint's Row may be hungering for. Remember, developers of this generation are used to working on multicore processors of 3.2GHz+ and hot garbage for GPUs so you may feel a squeeze from console ports even if they are ported reasonably well. People are just happy that the day of PC ports that are so bad, that it runs better if you emulate the console version, are mostly gone.

I'd imagine that you would have to figure this out on a case by case basis, i.e. the reason Saints Row The Third doesn't run so well and the reason something else doesn't run so well might be very different.

Thanks everyone for the responses. I had fallen away from PC games for a long time until I bought this laptop. I'm a little bummed that there is still the issues of "I wonder if this will work" with PC gaming. I'm not naive enough to think that every game would work exactly the same as every other game on my laptop. But I was expecting a little more parity.

This is why I only play non-graphic intensive games on the PC. I never know what the fuck is going on and why shit doesn't want to always work. Can't wait for the new consoles.