2 turbo's a week - 1 hour hard interval sessions. Look at trainer road for ideas.. or club etc Ideally these should progress as the weeks go by, so not the same thing each week I end up doing some spin classes but just destroy myself in them, (and ignore any crap teaching!)
Sunday long ride - regular stuff over the winter as you are doing, then as the weather improves, build distance up so 6 hr rides are not a problem for you. Don't do these at your target pace - keep your hr at your z2 (130 for me). You are building your endurance, not speed in these rides.
On some weekends, do some 3 hr 90k fast rides, and later on, do 90min easy, 1hr hard, 1 hr easy, 1 hr hard, 90 mins easy.
a second medium ride in the week can help, (ie 3 hrs on a wednesday? - i've never done that but its a suggestion i've seen)
In the last 6 weeks do a couple of big days - 5 hr/150k ride then a 60 min run. That will help determine your best biking pace, (probably slower than you expect)
Finally a 6:30 bike may give you a 3:45 run a 6:00 bike may give you a 4:45 run a 5:30 bike may give you a 5:45 run