[c-nsp] tx-ring-limit tuning

[C]

I'm Interested in trying to tune the tx-ring-limit for a number of ATM VCs 
that we have in our network to try and get the most utilisation out of them, 
currently they appear to hit the wall (we see performance degradation) at 
about 75% capacity in the transmit(tx) direction.

Hardware is: 7206VXR NPE-G1 populated with multiple PA-A3-OC3SMI

Is anyone able to provide a formula for better tuning the tx-ring-limit 
values for high-speed data VCs or provide suggested tx-ring-limit values for 
the following SCR sizes (where SCR=PCR):

16384 Kbps (38642 cps)
32768 Kbps (77284 cps)
36181 Kbps (85333 cps)
65536 Kbps (154567 cps)
72361 Kbps (170663 cps)

Cheers
[A]