Personally, I used to ran a Trinity D3.5 5.5 in my 4WD. For indoor (carpet/astro) it was just too much (for my driving skills
) motor, outdoor it's perfect and very fast.
If you like Orion, why not go 5.5 Orion? A motor won't make you seconds faster, buy what you'd like to run. I switch between Muchmore and Trinity and like both brands.