Js share my experience as well as I am viva 850 driver as well xD
I do travel alots and drove many car before frm 660cc to 3000cc
Wat I can say is viva is a quite good car in term of price and FC

My stock viva wif 12" stock rim with the ugly wheel cap plus stock silverstone 155/55/r12 can goes up to max 165km/h , I usually will pump ron97 if I travel frm kl to Ipoh/Penang...wat to say is , frm 0 to 100 ard 10 sec...by frm 100 to 160 will take minutes depend on the road slope..
Bt once I reach 1xx , I dislike to press brake otherwise pickup will really take time and when I flash high beam and overtake car , sense of accomplishment will full fill me xD

Last month I frm stock rim changed to 14 sport rim + Goodyear duraplus 165/55/r14 I felt that car is no longer stable n shaking than my 12" stock rims T.T....and the grip also abit loose , is it the tyre problem or rim size problem or absorber/spring problem?...
And also the steering is not hard and solid like before , especially during corner , felt that front wheel will auto turn abit and loose