I'm using 4s with the 4600 in my Rustler. It's under the 65k RPM limit with the batteries giving 3.5v/cell. Granted, it's not the best setup, but it's within the limits.
You could try contacting Team Associated about this issue and see what they say.
http://teamassociated.com/feedbackre...contacting.htm
SH Z-Car, Custom Crawler, 8s Savage,
12s XTM XLB 1/7 buggy,
4wd 4-link rear/IFS Pro4 truck,
Custom Hyper 10 Short Course,
Belt-Drive Mammoth ST 1/8 truggy, 4s 17.5 MM Pro HPI Blitz