I'm running an LRP28S3 in mine and really like it. However, going with that or the picco makes drive train maintenance become a bit more involved. With a weaker engine, your wheel hex's, diff cups, diffs ring/pinion, axles, slippers and spurs all hold up longer.
The first thing to go on my savage were both diffs. Bit the bullet up front and bought alloy diff housings (gear box's) and XL diffs. The XL diff ring/pinions appear to be machined vs cast like the old HPI diff gears. Hopefully with proper shimming, they will hold up for a decent while.
Now, I'm noticing a lot of wear on my center drive cups. Both front and rear are notched pretty badly and I have less than a gallon of run time.
I'm running 16/49 gearing with I believe the standard 3-speed. Bought it used, so I don't know if it has the high speed 3rd gear or not. When it shifts from 2nd to 3rd, there is noticeably more speed, but it isn't a huge jump, so I'd guess I have the standard ratio gears.
Tire choice also plays a part. Running the stock savage tires you have causes a lot of side roll, but it also gives you a higher top speed than standard MT sized tires due to the larger diameter. Larger sidewall tires make for a more cushy landing on the big jumps. For me, that softness is proffered over handling since I'm just usually driving by myself anyway. Thinner sidewall tires (40 series rims w/ appropriate tires) will give you better handling, but will abuse your shocks a bit more due to not absorbing as much impact.
Running the wheels you have with stock hex's will not last long at all with a higher power engine. I upgraded mine to standard sized RPM MT wheels but with 17mm hex's. I bought the hex's/nuts for the XL only to realize that HPI did away with the reverse thread axles on one side of the XL, so I had to order two new stub axles. Hopefully I won't go through wheel hex's like I did last year with my aftershock (also 14mm at the moment). It is also sporting an LRP, but it's first gear is quite a bit taller than the savage first gear, but it's second tops out earlier than the savage's 3rd gear. Regardless, it's low end torque is less due to the taller gear ratio in 1st, so if it was burning up hex's last year, the savage wouldn't make it through a weekend without shelling one on me.
Anyway, my setup:
LRP28S3 for an engine
16/49 CB/spur
25% byrons fuel
Losi HT pipe (runs really good with the LRP)
RPM 17MM rims w/Savage21 tires
HB 1" extended chassis
XL diffs
XL brakes
The thing does really great in pretty tall grass and it's top speed on pavement is pretty much uncontrollable. Any deviation from a straight line at WOT will send it out of control. Wheelies are also effortless. To the point that they are irritating.
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but since we will probebly never run together