Hi amyL
A handful of good members have already given you some useful information I think, but I hope that I can add a little.
I have the BCS 740 with the new PowerSafe clutch. This model is almost identical to the 749 sold in the US, except for longer handlebars and a few other things, as I understand. These two models do not have the transport gear, which the models 852/853 with the traditional cone clutch have. The differences between the two different types of clutches are discussed in this thread:
http://www.tractorbynet.com/forums/2-wheeled-tractors/231657-powersafe-clutch-bcs.html
The transport gear allow much higher speeds than the 3 working gears, and is therefore ideal when you have to transport the tractor between more working places, as it allows you to walk with the engine at idle, instead of full throttle in 3rd gear. Note, that the transport gear only allows you to drive in
one direction; forward in the front-PTO (mower) mode for the 852, and forward in the rear-PTO (tiller) mode for the 853. This means, that if you plan to use a trailer or rear mounted implements, you are better off with the 853. If you use more front mounted implements, the 852 might be your best option. Joel explains these differences in more detail here:
Earth Tools
You will find useful information on wheel/tire size in a number of threads, like:
http://www.tractorbynet.com/forums/2-wheeled-tractors/322759-larger-tire-options-bcs-852-a.html
http://www.tractorbynet.com/forums/...3-tire-size-width.html?highlight=#post3329505
As you can see in the threads mentioned above, choosing the right wheel size depends on which implements you plan to use. For tilling smaller wheels might be the right choice, as larger wheels might tilt the tractor too much. I use my 740 for mowing and sweeping, and for those jobs - and perhaps most jobs in the front-PTO mode - I can highly recommend the largest possible wheels. Had I known better when I bought my tractor, I had bought it with the 6.5x12x23" wheels straight away, as I have no use for the smaller standard wheels.
Just to make sure we are talking about the same: when you say 10" and 12" tires, these numbers are the diameters of the rims. The outer diameter of the tires mounted on these rims are usually 20" and 23" respectively, depending on width and construction.
Foam serves two goals: added weight for better traction, and less risk of a puncture.
I have no experience with foam, but if you are looking for weight, I can also recommend wheel weights. I use 15 kg (33 lbs.) in each wheel all the time, and it makes a lot of difference on traction and stability.
Best regards
Jens