grip/braking/handling of a stock 5th and 6th gen or a modified one??? 
Second, talking about stock, u cannot surpass the grip/handling/braking of a 5th and 6th gen civic as compared to the 4th gen.
Third, if talking about modified version, it depends on all physical performance related parts you install even in a 4th gen, 5th gen, 6th gen civics. in this case ur stock parameters obsolete related to grip/braking/handling whether of 4th or 5th or 6th gen civics.
we have modified numerous of 6th gen civics (performance related) here in KHI, the fastest civics ever in Karachi are the 5th and 6th gen, not even a single 4th gen civic had ever blasted the tracks here. Details of modification commonly done in our civics are as below.
Engine:
B16 Bottom End Build
D16Y8 Intake Manifold onto a D16Z6
'96-'00 SOHC Mini-me
Installing Energy Suspension Polyurethane Shifter Bushings PART 1, PART 2
Rebuild/Fix FITV
Rebuild/Fix FITV #2
Timing Belt and Water Pump
Coolant Flush and Thermostat Change
Changing Distributor O Ring
DOHC VTEC Valves, Valve Springs, and Retainers replacement
D Series Valve Springs Install
D Series Valve Lash Adjustment
Changing Header
Installing B&M Fuel Pressure Regulator
Removing Crank Pulley
Leak Down Test
Build Your Own Leakdown Tester
Seafoam: Experience and How-To
Converting JDM Intake Manifold To Meet USDM Cali Ref Specs
Making JDM ITR Motor BAR Legal
B-Series Valve Adjustment
D16Z6 head onto a D16Y7/D16Y5/D16Y8 block OR D16Y8 head on a D15B7/D16Z6 block HEAD BOLTS STUDS EXP
BLOX Intake Manifold Installation
Transmission:
'96-'00 Auto to Manual Conversion
D Series Transmission Tear Down
Changing Transmission Fluid
Short Shifter Install
Short Shifter Install
Suspension/Brakes/Steering/Running Gear:
This pertains to anything "under" the car, struts, sway bars, rack & pinion, rotors, axles, so on and so forth.
Basic Brake Component and Upgrades (Ventilated discs)
B Series Axle Replacement
Power to Manual Steering
ITR Brakes Onto '96- Civic
Integra Brake Swap Onto '96
Changing Tie Rod Ends
Fixing Camber With Washers
Traction Bar Install On '96-
HX Rims on GSR/Si
Front Strut Tower Bar Installation
'96-'00 Civic Lower Tie Brace Installation
Installing Coilover Springs
Installing Lowering Springs
NSX Calipers on '96-'00 Civics
Replacing Brake Rotors
Integra Disc Brake Conversion Using Stock Knuckles
1" JDM ITR Master Cylinder and Brake Booster Install
Changing Brake Pads and Rotors On '96
DIY Replacing Trailing Arm Bushings
Popping Front Ball Joints Out
Installing ARP Wheel Studs