Oracle RAC - Any formula to calculate/preempt the right number of LMS processes?

We are on 10gR2 5 node RAC (a huge and very busy DB) and also very high number of CPUs (80ish) hence the default number of LMS processes that Oracle generates for us (num_cpu dependant) is way too high and is causing CPU consumption issue (due to their high priority) for some time now so we need to look to reduce (and fix) them to a sensible number and going by RAC expert Riyaz's advice we shud reduce them down to 4 (one for each 'other' RAC node) which makes sense to us particularly becs if we were going 11g and left this parameter to Oracle's default calculation it'll come down to 3. (Current number of LMS processes : (Due to the varied number of CPUs ) - On 2 nodes, 10, on 1 12 and on the other 2 : 8).

Moreover, we've done the analysis and there are no major RAC wait events (as in we are not much suffering from RAC) and we "think" we should be fine by reducing these and obviously we'll take them thru to Performance Test to gain some confidence.

However the question is, is there any other mathematical way of getting to just the right number of LMS processes for a RAC instance pls? Is there any formula to predict them or even to predict if there will be any latency impact by reducing these?

Thanks in advance.

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