I tried to play “Fun 2 Step.rns” that I found on SONGS page today. [It’s a nice Chip Tune!!]
But I couldn’t listen smoothly in Ver.1.281 on my PC.[AMD Duron 1100MHz]
Then I tried to play it in Ver.1.5a4…
Wah! I was able to enjoy it very smoothly!! 
Probably the rate of CPU use is decreasing about 20~30%.
Great!! A lot of THANKS for the Renoise Team.