The last gen Merc E is not £300 better than the Insignia imo, bank the money.
Ive been trying a few Volvo's, the V60 through our scheme can be had for £140 ish all in (im a 20% tax payer though), £200 gets me in a XC60 R design. You must have been paying a fair old chunk for the Merc, as ive never really seen them that well priced on company car schemes for any company ive worked for. The superb is pricey on our scheme, there dont seem to be decent discounts on em according to the dealer.
Pity you cant get Jags, as the XF seems to be a decent deal at the mo, ive just handed back a XF demo and it was a top top motor. Nicer than the A6 i had last week.