For me, it depends on what the opposition have got. Presuming this is a league game and you know the side you're playing and their strengths, when you have 8-9 players (as we did a couple of weeks ago) you act according to those.
Its all very well saying you don't worry about the opposition, but I feel you have to with less players. To use my actual scenario, we won the toss and batted with 9, inc. 2 mates of players, who were hardly capable cricketers. Got to 140-odd all out and although we had them 60-6, they got to the target with 3 wickets to spare. On average we lost 30 runs from having 2 less players and probably another 40 in the field, not to mention the psychological effect of having less players. Overall, two evenly matched sides who we would have beaten with our full side. We were two bats and a bowler short.
We had 2 decent bowlers (as 60-6 suggests) and 3-4 capable of scoring runs, of which two hit 30 and 50-odd. Similar to your hypothesis and it turned out close. So I'd look at what the opposition have got...