You should see some nice scalability improvements in 3.8 and within 4.0 (prior to that the scalability was limited to around 800 relationships, but that assumed an acceptable GUI response time cut off at 8 secs
I have attached at updated sizing guide which was done post 4.0 (available at - http://media.netapp.com/documents/tr-3440.pdf😞
Section 6.1.3 (4.0 testing ) and 6.2.2 (3.8 testing) are probably of the most interest but also check out the Summary for some recommendations there as well, also note these loads where conducted with Performance Advisor segregated to a different instance;
Cheers
rich