I would choose the 3500+ over the 3800+ easily any day. They will perform nearly on par with one another and a 3500+ can easily surpass a 3800+ with the right know how.
The 3500+ is a good chip, if you want more performance, pick a 4000+, double the cache plus increased clock speed will make boast performance a lot.
Basically, more performance, go with the 4000+. Better value is the 3500+ hands down.