I recently made a 100% RedX beer (well, 100% base malt along with some british crystal and Special B) and I probably should have mashed it lower than 150 because it's very malty and it doesn't finish quite as dry as I would like.
First off, I would implicate the British Crystal and Special B as the likely culprits for your beer not finishing as dry as you'd like.
I recently brewed a mainly Red X hoppy lager that finished very crisp and dry. Since Red X has a similar diastatic power to Munich malt, it will convert itself, but I like to include a small amount of Pilsner malt to boost the enzyme content (since I BIAB, my mash is pretty thin - this may not be necessary on everyone else's system). I mashed at 149F, which is a few degrees lower than my usual 153F, but not as low as I go for Belgian ales or really big barleywines. I targeted 120PPM of sulfate, which is noticable but not crazy high. IBU's were probably in the 40-45 range (I made some last-minute substitutions, so I don't recall the exact amount).
Anyways, sorry for the rambling respone to your rambling question
Basically, mash temp was just a small portion of the steps I took to ensure that my beer finished as dry as I wanted. Grist is probably the biggest factor, but mash time/temp (and knowing how that works in relation to your system), water treatment, and hop selection and usage all come into play. You can pick any one of these factors to adjust if you want to help dry out your recipes. Depending on your system, mash temp doesn't necessarily need to be the first choice.