SariPac is indeed closer to most of the key attractions including Monas (it will eventually be one stop away on the MRT when the station directly in front of the hotel opens). If you are comparing locations, as several FTers have noted, The Hermitage is a nice, quiet area that's actually pleasant to walk around in, but there's really nothing to walk to. Not that I'm saying you should walk from SariPac to Monas, but that the property definitely has the edge on location. Jakarta traffic is as bad as ever right now.
Might want to check again as several hotels have repriced, presumably due to lower demand over Ramadan. For your dates, I'm seeing a senior rate at SariPac of 6.3 million IDR.
I recently completed a 4-night stay at The Hermitage, which was just about enough. May or may not review it, as I don't have much to add to what's already been documented in the property thread.
From reading about the issues popping up with your KL stay, and other criteria you've mentioned (whirlpool, a good club lounge), you may want to consider splurging for your last (Friday) night at The Westin where weekend rates this March are the lowest I've seen in a long time at IDR 2 million/night (senior) and ~1,9 million/night (AAA).