I'm with vtsteam. I have a Sieg C3, like your 7 x 10, only 7 x 13ish. I used a 35mm diameter post, to keep things as stiff as possible, bought the 50mm x 50mm free machining bar as 25 mm slices off the square bar. Then spent a fair bit of time making all the toolholders, I'm now up to about 20.
The 35mm bore in each toolholder was done carefully to minimise the amount of deflection when clamping, this increases the area in contact between the post and toolholder. Which in turn makes the whole set up stiffer. Two clamping screws were used to make sure, on reflection they could probably have used only one.
The main aim of all this was to reduce chatter and make parting off easier. Chatter has certainly been reduced considerably, and parting off is now a piece of cake. This morning I was parting off 20mm diameter cast iron at 200rpm, al. alloy is regularly parted off at up to 700rpm depending on diameter. The big advantage of a 7 x ?? machine is that paring off can be done with the spindle running backwards, with the p/o tool upside down.
cheers
Bill