I had to go look at the book. It is a BE-55 and the numbers we were using were in MPH. Vlo is 150 mph and Vle is 165. So that wasn't an issue. The book I have here does not have the "approach flaps" number(or any other for that matter). What amount of flaps is it that you use Dave?
Yea, that always messed me up when flying the older 55s, but on some, there is also a knots marking on the indicator. 120 is a great speed because it converts to rate of descent so easily; as has been said, five times on the GS equals 600 fpm in a no wind condition.
The P-Baron has an approach flap position which is 15 degrees. One can go around with these flaps in and get a decent rate of climb on one engine (I'm not suggesting this); they slow the plane without adding the drag of full flaps. Approach flaps in the P can be deployed at 177 IAS below 21,000.
I completely agree with the point being made about slowing before the IAF or at least well before you will be making a decent. Some GPS approaches have long legs with little or no decent. I have the plane at 21" of MP, approach flaps and slowed to near 120 IAS before I will be descending. On an ILS, about 5 miles from GS intercept I put it in the approach configuration. When I intercept the GS, all I have to do is pitch down a couple degrees and extend the gear.
On long legs of a gps, I may keep speed up until 5 miles from FAF if the initial leg is level. Once again, 5 miles from the FAF or where the descent will begin, initial approach configuration.
What used to happen at KSEE (San Diego, Gillespie) was there was a long decent from the intersection off the airway (Baret) with step down fixes. If I came off the airway at cruise speed and immediately began a decent, airspeed would get high and rate of decent would go up. Good VFR day or high ceilings, I'd just keep power up, nose over clean and reduce power later, raise the nose, extend the gear and put in approach flaps. If it was low IMC, I'd slow down about 5 miles from Baret on the airway and put it in the initial landing configuration. Seemed to take forever to get down at 120 knots, but completing the approach was first and foremost.
Barons have a wonderful ability to lose altitude if need be: as Bob said, props forward, MP back, approach flaps and a slip if it's VMC. I can come down 4,000fps straight ahead as stated above. Put in a slip and you can come down more.
Sounds to me as if you just need to get used to the speed and configuration. I'd really suggest you try a couple with approach flaps and without. Most folks I know that fly the 55 don't use approach flaps, but you should know what they can do for you and when they could be helpful. Practice two approach speeds: 120 and one faster, say 150. Not for your ATP ride, but for practical reasons when mixing with faster traffic.
Best,
Dave