Either can do the tasks you mentioned, but the 4300 will probably do them with less effort if they are heavy-duty or above average in quantity or size. You might not push even the 4200 to its limits very often.
+ For 4300... Takes the 430 loader, which has better performance than the 420.
+ For 4300... Will take up to a 6-foot light duty, or 5-foot medium-duty rotary cutter... 4200 takes 5-foot light duty max.
+ For 4300 if a backhoe is a remote possibility at any time during your ownership of the tractor... The 4300 takes the 48, while the 4200 takes the 47.
The 4300 is slightly larger, heavier, with higher hydraulic flow, and about 500lbs more 3-point lifting capacity. 4300 also has the optional 12x12 SyncReverser if you're not a 'hydro man'.
Basically, you get what you pay for if you do upgrade to the 4300. But the real question is not that, but rather if you need the extra power/capability.
It is common to see folks upsize... and upsize. Sometimes the extra power goes unused and isn't really needed for the realistic, common chores you'll use the tractor for. Since the choice is yours, can you justify extra cost for extra power that might be there just for fun? I wouldn't doubt the 4200's ability to serve the needs you described.
Hope this helps...