Run the piano at Medium key touch setting, try the Classic piano patch (I think it's the same samples as the GrandX), make sure there is no MFX enabled (they often put the Enhancer on as default, which overly brightens the sound).

In all fairness, I don't use ANY piano patch in the G70 other than the GrandX (and occasionally a honky-tonk), I don't like them much at all. But one PERFECT piano is all you need, IMO!

Strangely, most at roland-arranger.com complain the the Roland pianos (at least the Classic and Superior) in the E50/60 are too DARK for them, and from what I heard (there's a thread from a while ago where we ran the Purgatory Creek file through those patches), I tend to agree. We discussed ways in the voice programming (adding a bit to the cutoff value seemed to work) to get them back to the G70's sound. It might help.

My take was that many had come from Yamaha and Korg arrangers and keyboards previously, which IMO are WAY to brittle and bright, compared with a REAL piano, and were hooked on that tinny sound.

BTW, you didn't answer the question... Which piano sound ARE you using?

As to the piano 'spiking' on some hits, well, that sounds a LOT more like a touch issue. Do you use High as the touch setting? Try Medium. Do you have 'spiking' issues on other sounds? If not, there's nothing wrong with the keyboard. I presume it is not just one note that is jumping out (otherwise it might be a key contact problem).

Just how good is your playing touch? Record something into the sequencer, and take a look in a graphical sequencer (it's a lot easier than looking down the data list) after you transfer the SMF. Do you notice any unusual jumps? It sometimes helps to analyze your playing this way, to see if certain licks or playing styles make you whack the keyboard harder, and adjust your playing accordingly.

Me, I'd stay off everything other than the Superior, Natural and Classic pianos, just because they don't have the velocity layers that those three do.

Hope this helps.