I ran your numbers in a calculator and the 69 plate is coming out at £412 a month, not £301.
48 x £301 = £14,448
Plus balloon of £11,500. Total= £25,948.
That's less than the £27,400 you mention, and doesn't even take into account any interest. Is there some huge incentive somewhere? Am I misunderstanding?
Personally, I'd take the older car and try and finance elsewhere, rather than PCP. Money Saving Expert is showing car loans for up to £25K (you'll need to find a couple of grand to cover the rest up to £27.4K) for 2.8%, vs. 4.9% you're being quoted by Lexus. Over 4 years, that's nearly £1,700 in interest savings alone. Of course both scenarios are subject to passing credit check which may be easier to do at the dealer perhaps.
You seem adamant on paying the balloon and keeping the car, so take a loan for it.