Yes, it will absolutely be sufficient for running office software and web browsing.
When I purchased my first work machine, just about 5 years ago, I ordered a Fujitsu because they were the only major vendor offering what was, at the time, the best mobile CPU on the market (best combination of power management and performance, IMO) -- the 2.8 GHz Intel P9700 Core2Duo. The i3 in the base model Surface tablet benchmarks about 10% higher than that chip.
For my money, the best value in the Surface Pro 3 lineup is the base i3 and a healthy-sized microSD card.
If money isn't much of an object, by all means jump up to the i5 with more storage.
If your computing needs really did require top performance, I'd probably suggest looking elsewhere, at something (1) with better heat management than an uber-thin tablet, (2) that you could bump up to 16GB+ RAM, and (3) with a user-accessible HDD, so you could install a high-performance SSD of your choice.