The running tools now include a Pace Calculator. Enter how long one km (or one mile) takes and it shows your speed and the pace in the other unit, plus your finish times for 5K, 10K, half and full marathon at once.
If your marathon time beats sub-3 or sub-4, a badge tells you right away, which makes it easy to pick a race pace. You can paste a pace like 5:30 or use the ↑ ↓ keys to try paces one second at a time.