If AC cannot be done for you due to the specs, then get GTR2 or rF1. Of the simBin titles, GTR2 is the best there is (with full weather and day and night cycle), later incarnations all had more or less serious disadvantages compared to GTR2. Good AI (still so!), an for the standards of when it came out very good driving model. Also, at NoGripRacing there is practically no track or car that cannot be had has a mod. Some of them really look extremely good.
When GTR2 came out, I was very enthusiastic about it. It's just that simulation technology has gone beyond those old standards form back then. Against iR, AC and probably also rF2, it stands no chance.
In principle, I recommend AC. For older hardware, I recommend GTR2. NFS and such titles I do not take as serious attempts of simulating something.
GTR2 can be had for less than 5 bucks by now. Watch out for the opportunity.
P.S. Evolution and Race 07 have no night-day cycle and no weather.
P.P.S. You can check for GSC2013. It uses the graphics engine from the first rFactor, just has much better physics, and a nice Nordschleife mod. How could I miss to list that? GSC2013 is the way to go, no doubt, if hardware specs allow it for yo9u. Check this thread and its videos, the karts are GREAT FUN and are very well done, physics wise.
http://www.subsim.com/radioroom/show...=211174&page=2
This is their official specs:
Minimum configuration: 1.4 Ghz Processor / Windows XP or superior / 1GB RAM / Directx 9.0c compatible video card with 256MB Video RAM / 4 GB free hard disk space / Internet connection for online activation
Recommended configuration: 2.6 Ghz Processor / Windows XP or superior / 2GB RAM / Directx 9.0c compatible video card with 512MB Video RAM / 4 GB free hard disk space / Internet connection for online activation
PPP.S
As Herr Berbunch said, there also is netKart Pro, very cheap by now. Good physics but - if you do not do MP, you will race alone, since there are no AI cars. It looks dated by now, however. A solid track collection can be build via free downloads. The guys behind nKp are the same who now do AC.