I run a 1920/8 with a micro2095 and have no issues at all......I've been running the same motor for 4 yrs......it's a very good motor...the 1920/5 ....has the following rpm per volt......
1920/5Hi-Amp Motor LMT RPM per Volt 6270, max. 65.000 U/min., 850 Watt, 170 g.....
just keep that in mind, for the controller I recomend.. a micro20120
A 7 turn or 8 turn on 3s would be very quick,but to have a motor that can run on 2s and 3s isn't ideal,because it's a 3rd difference in rpm.You'd have to have it very mild on 2s (say 30,000 rpm) so it wouldn't be too hot on 3s.
Easier on 3s and 4s though,i have a 1920/10 that runs good on both.
I thought Mike has some 4mm pinions,if not then get someone with a lathe (such as Mike)to run a 4mm drill through some 1/8 pinions,i do that to run 48p pinions on my 1920,there's still plenty of meat left on them since you're only increasing the diameter by less than 1 mm.
Yea, theres this guy called Mike. You can contact him on his site, http://www.rc-monster.com/ Oh, by the way, they have a GREAT forum with alot of helpful people.
Mike can order you one and accepts paypal but they usually take a few weeks to arrive from Germany.E-mail Mike,when i got my 1920 he had a few in stock,just not listed in the store.
The 6 turn is nearly 60,000 rpm on 3s though,it might get a tad warm so to speak,could be fine though(definately VERY fast) but i've never revved one that high so i don't know.