i run 10k in the front 7k in rear that should be a good starting point. the thicker fluid in the front gives you more on power steering and less off power.
I am using 10K front and 5K rear in my t-maxx conversion
1. MBX-6 T8 1900KV, RX8 ON 4S
2. MBX-5T 1520, MMM ON 5S
3. MBX-5 ONROAD CONVERSION 1515, MMM ON 5S
4. MRX-3 ON ROAD CONVERSION 1512, MMM ON 6S
5. TEN T 2650 T8, MMP ON 3S
I'm using 7000 in the front and 5000 in the rear. Mike recommended this setup (for what it worth). As stated above thicker fluid in the front gives you more on power steering and less off power.