Menara Imperium is on Jalan Rasuna Said. It's actually within about 5 minutes walk of the FS, so that's probably your best bet. It's really just across the road.
The IC, Shangri-La, Grand Hyatt, Marriott Mayflower Apartments, and the new Hotel Indonesia Kempinski are all close by. However in peak hours it'd probably take 20-30 minutes because of traffic and a whole series of one-way streets.
The LM is probably about 10 minutes further away as are the RC and the JW Marriott (although in another direction).
If the choice is just on location the FS is the best choice by far. It's also a lovely hotel. There is also a small complex of apartments called The Kuningan Suites right next to the FS if you want the location without the cost.
http://www.jakarta-cityhotels.com/ho...ningan-suites/