For the buses, PikkaBird's HOVS bus set performs quite well, and I always use it when playing with the road vehicle acceleration patch on.
For the standard buses and trucks, I have "guessed" the following values, which are hardcoded in the realistic acceleration patch. The values are not wildly guessed, but they are such that the vehicles in question reach their maximum speed even when fully loaded (at least they should).
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weight (kg) power (hp)
MPS Regal Bus 8000 100
Hereford Leopard Bus 9500 190
Foster Bus 10500 290
Foster MkII Superbus 12000 400
1st generation truck 9000 150
2nd generation truck 12000 260
3rd generation truck 13500 380
The trucks of the default vehicle set hence all have the same weight and power rating, regardless of their cargo. This means a slight disadvantage for the vehicles that transport heavy cargo (e.g. bulk goods like coal, grain, iron/copper ore, etc.). This effect is the largest on inclined roads: Heavier vehicles will have more difficulty climbing a mountain. So perhaps for the GRVTS you should give the vehicles carrying heavy cargo and the articulated vehicles more power.
The values in this table are more or less in the region of comparable buses in the HOVS set and PikkaBird's suggestion in the previous post, although my values seem to be slightly higher (i.e., "my" vehicles are slightly heavier and more powerful). Unfortunately, I do not know how TTDPatch implements the weight and power for the default vehicle set (which should have been defined somewhere, since TTDPatch also contains realistic acceleration for road vehicles, as far as I know). Maybe you can try to obtain these values and use them as a suggestion as well?
As for the other properties: According to the grf specifications, one can also set the maxTE ratio and air drag coefficient for road vehicles (Action 0 properties 18 and 19). However (unlike power and weight), not setting the values for maxTE and air drag will give the vehicles default values, which works well most of the time (except maybe that you may want to lower the air drag coefficients for extremely fast buses, but as far as I have seen these are not included in GRVTS).